A Muslim imam and a second man were fatally shot on Saturday while walking home from afternoon prayers at a mosque in the New York City borough of Queens, authorities say.

Key points:

Men identified as imam Maulama Akonjee, 55, and his associate Thara Uddin, 64

Police say motive unknown, no evidence yet indicating men were targeted due to religion

The two men were wearing religious garb at time of shooting

The gunman approached the pair from behind after they left the Al-Furqan Jame Masjid mosque and shot both in the head at close range about 1:50pm (local time) in the Ozone Park neighbourhood, police said in a statement, adding that no arrests had been made.

Officers said the individual was still at large and the investigation was ongoing.

The victims, identified as imam Maulama Akonjee, 55, and Thara Uddin, 64, were both wearing religious garb at the time of the shooting, police said.

However police said the motive was unknown and no arrests had been made.

"There is nothing in the preliminary investigation to indicate that they were targeted because of their faith," police told journalists.

But Sarah Sayeed of the New York mayor's office insisted that "the NYPD is looking at all angles of this crime, including the hate crime (angle)".

The NYPD declined to describe the connection between the victims but the Council on American-Islamic Relations said Mr Uddin was an associate of the imam.

"The perpetrator of these senseless killings must be swiftly apprehended and face the full force of the law," Afaf Nasher, executive director of the Muslim advocacy group's New York chapter, said in a statement.

The men were transported to Jamaica Hospital Medical Centre and died "while life-saving procedures were being performed", hospital spokesman Andrew Rubin said.

The shooting comes amid a climate of growing Islamophobia and anti-Muslim sentiment as a series of deadly attacks have unfolded in the US and abroad, some of which have been claimed by the Islamic State group, and Republican presidential contender Donald Trump's proposal to ban Muslims from entering the US.

The working class area, on the border between Queens and Brooklyn, is home to many Muslim families from Bangladesh.

Slain Muslim cleric 'wouldn't hurt a fly'

Kobir Chowdhury, who heads the nearby Masjid Al-Aman mosque in Brooklyn, said: "Please, read my lips. This is a hate crime, no matter which way you look at it.

"It's hate against humanity, it's hate against Muslims, these are Islamophobes who are causing these kind of troubles."

Police have yet to identify a suspect but police said witnesses saw a lone man fleeing the scene with a gun in his hand.

The suspect was described by police as having a medium complexion and dressed in shorts and dark polo shirt.

"We are currently conducting an extensive canvass of the area for video and additional witnesses," Deputy Inspector Henry Sautner said in a statement.

Mr Akonjee was described as a peaceful man who was beloved within Ozone Park's large Muslim community.

"He would not hurt a fly," his nephew Rahi Majid, 26, told the New York Daily News.

"You would watch him come down the street and watch the peace he brings."

Video footage posted on YouTube showed dozens of men gathered near the site of the shooting, with one of them telling the crowd that it appeared to be a hate crime, even as police said the motive was still unknown.

Councillor says 'we must come together as a community'

"It's really threatening to us, threatening to our future, threatening to our mobility in our neighbourhood, and we're looking for the justice."

The neighbourhood's city council representative Eric Ulrich tweeted that he stood "in strong solidarity with all Muslim New Yorkers tonight as we mourn the killings of Imam Maulama Akonjee and Thara Uddin".

"When a religious leader is killed in broad daylight on the streets of Queens, we must come together as a community and demand justice!" he wrote.

Footage uploaded to Twitter showed people gathered Saturday evening near the scene of the fatal shooting, many of them yelling "we want justice".

"Imagine your father gunned down for no reason, and then let that feeling, let that motivate you to come out of your silence," Mr Nasher said.

"When we stay silent we allow crimes to continue to occur.

"So every single one of us shares in this responsibility. And let's not forget the victims who are essential to all of this."